This invention broadly relates to a communication network, a wavelength multiplexing device, an optical switch equipment, and an optical link attribute/state administering method for them.
More specifically, this invention is directed to a method for administering the attributes and states of optical links between transparent optical switch equipments in a communication network including a number of optical switch equipments connected with each other by using WDM (Wavelength Division Multiplex) transmission equipments.
In a conventional trunk optical communication network, a plurality of optical switch equipments are mutually connected in a mesh-shape via optical fibers. On these optical fibers, signals, which are wave-multiplexed by the use of a WDM transmission equipment, are transmitted. Herein, the wavelength multiplexing number per optical fiber is equal to 100 at the maximum.
The above-mentioned optical switch equipments are classified into two types. One type corresponds to an opaque optical switch equipment which once photo-electrically converts an optical signal into an electric signal via interfaces. In the opaque optical switch equipment, electric signal processing thereof is restricted in signal rate to a constant value. However, control signals can be easily and advantageously exchanged between optical switch equipments.
Another type corresponds to a transparent optical switch equipment without use of photo-electric conversion. In such a transparent optical switch equipment, general switching of wavelength-multiplexed signals as well as switching for signals of an arbitrary signal rate or signal format can be carried out advantageously. On the contrary, the control signals can not be readily exchanged between the optical switches without the electric signal processing.
Under above-described circumstance, the optical switch equipment functions as to the transparent optical switch equipment for some interfaces. The optical switch serves as the transparent optical switch in a wide sense even when the electric signals are processed via the other interface. The transparent optical switch normally serves as a part of optical fibers, and therefore is seldom switched as a switch device.
The optical switch equipment is connected not only with another optical switch equipment but also with a device acting as a client of the trunk optical communication network, such as the SONET (Synchronous Optical Network), the ATM (Asynchronous Transfer Mode) switch and the IP (Internet Protocol) router.
The trunk optical communication network provides optical paths between a plurality of client devices by employing one or more wavelengths. The optical paths are set up so as to lead from an input optical switch equipment connected with a client device through a plurality of relay optical switch equipment to an output optical switch equipment connected with another client device.
In such a trunk optical communication network, the optical paths are administered in dependency upon multiple administrative hierarchies. These administrative hierarchies include an optical path section between client devices, an optical path relay section between wavelength converters or 3R (Reshaping, Retiming and Regeneration) regenerating relays, an optical-multiplex-section (OMS) between WDM transmission equipments, and an optical-transmission-section (OTS) between optical amplifiers (amplifiers).
According to these administrative hierarchies, administrations are performed so as to set up or release optical paths and to detect or recover faults. As illustrated in FIG. 1, one optical path relay section of a wavelength λ1 is defined between an opaque optical switch equipment #1 and an opaque optical switch equipment #3, each having a wavelength converter. This optical path relay section includes a transparent optical switch equipment #2 and two optical multiplex sections.
Referring to FIG. 1, wavelength converters 70 to 75 and WDM transmission equipments 91, 92 are connected between the opaque optical switch equipment #1 and the transparent optical switch equipment #2 via the optical amplifier #1. While, the WDM transmission equipments 93 and 94 are connected between the transparent optical switch equipment #2 and the opaque optical switch equipment #3 through the optical amplifier #2. Herein, it is noted that reference numerals 80 to 85 designate wavelength converters, and reference numerals 90 and 95 designate WDM transmission equipments, respectively. Meanwhile, the technique for administering the network according to such administrative hierarchies is disclosed in Japanese Unexamined Patent Publication No. 2000-183853.
In the above-mentioned trunk optical communication network, the optical paths are dynamically set up and released on the basis of a demand from a client device. The route control softwares installed on the respective optical switch equipments compute or calculate an optimum optical path route reaching the optical switch equipment connected with an address client device, thereby producing a route table describing the corresponding relations with respect to output interfaces between an optical switch equipment connected with the address client device and an own optical switch equipment for setting up the route of the optical path.
The computed optical paths are set up and released for every hierarchies in accordance with the administrative layer. In the system shown in FIG. 1, for example, the relay optical switch equipments #1 and #3 along the optical path are selected so as to set up and released the optical paths in the optical path relay section, thus setting up the optical path relay section to the wavelength λ1. The setup of the optical switch equipment is carried out on the control channel, which is preliminarily provided between the optical switch equipments, by exchanging the control messages with respect to the address or the identification No. of the optical path mutually. Herein, the technique of this control channel is disclosed in Japanese Unexamined Patent Publication No. 2000-004460.
In the above-described conventional communication network, however, no administrative hierarchy for administering the sections between adjoining optical switch equipments exists, Consequently, the transparent optical switch equipment will be administratively regarded as a part of the optical fibers laid in the optical path relay section even when the transparent optical switch equipment exists in the optical path relay section, as illustrated in FIG. 1. This makes it impossible to recognize the section between the interface of the transparent optical switch equipment and the interface of the adjoining optical switch equipment, as an administration target independent as the optical link. Not only the transparent optical switch equipment but also the aforementioned optical link is not recognized as the setting target during setting up and releaseing the optical path.
In the control channel, which is preliminarily provided separately of the optical link between the optical switch equipments, the control message cannot be exchanged for every optical links. Further, such a control channel is not arranged between the optical switch equipment and the WDM transmission equipment contained in the optical multiplex section. Therefore, the control message cannot be exchanged between the optical switch equipment and the optical multiplex section. Moreover, the optical switch equipment cannot obtain information upon the attributes of the optical link specified by the optical multiplex section. Accordingly, the automatic discovery of the attributes and the administration of the state of the optical link specified by both the adjoining optical switch equipments and the optical multiplex section cannot be carried out by utilizing the conventional technique of the control channel.
In addition, the attributes of the optical link between the optical switch equipments cannot be discovered. Therefore, the mutual connection relations between the interfaces of the optical switch equipments cannot be autonomously discovered so that the route control software cannot produce the route table automatically.
Therefore, in the case where at least one of two adjoining optical switch equipments corresponds to the transparent optical switch equipment, the attributes of the optical link leading from the output interfaces (IF) of the optical switch equipment through the optical multiplex section to the input interfaces of the adjoining optical switch equipment can not be automatically discovered to administer the state at the unit of optical link.
Further, when the optical switch equipment sets up the optical path to another optical switch equipment, the optical switch equipment cannot autonomously determine an output interface to be employed. Therefore, it is necessary to manually set up the route table describing the corresponding relations between the optical switch equipment connected with an address client device and the output interfaces of an own optical switch equipment for setting up the route of the optical path.